1. Technical Field of the Invention
The present invention relates to a turbocharger with a variable nozzle, and more particularly to a turbo charger with a variable nozzle having a mechanism capable of suppressing a temperature increase of a compressor side thrust bearing or the like.
2. Description of the Related Art
A turbocharger is a supercharger used for a high output of an engine, for example, for a motor vehicle. In the turbocharger, a compressed air is supplied to the engine from a compressor by rotating a turbine impeller by exhaust energy of the engine, and rotating a compressor impeller by an output of the turbine. Accordingly, it is possible to achieve a supercharging state over a natural air supply in the engine.
In the turbocharger, at the time of low speed revolution of the engine, the turbine hardly works due to a low exhaust flow rate. Accordingly, in the engine capable of operating at a high speed revolution, it takes a long time until the turbine efficiently rotates, so that it is impossible to quickly obtain a turbo effect.
Accordingly, there has been developed a turbocharger with a variable nozzle (a variable geometry system turbocharger (VGS)) which is efficiently activated even from a low speed revolution range of the engine. The turbocharger with the variable nozzle is structured such that a high output can be obtained even at a time of a low speed revolution, by throttling a small exhaust flow by a movable vane, increasing a speed of the exhaust gas and enlarging a work load of the turbine. The turbocharger with the variable nozzle as mentioned above is described, for example, in Japanese Examined Patent Publication No. 7-13468 “turbocharger”.
However, in the turbocharger with the variable nozzle, there is a problem that a temperature of a thrust bearing provided in a compressor side of a bearing housing gets over a critical temperature 250° C. so as to be increased to about 300° C. due to a heat transmission (a heat soak) from a turbine side of the bearing housing to the compressor side, at a time when the engine stops and a pressure oil cooling the bearing housing stops. Meanwhile, the problem mentioned above is not particularly pointed out in the turbocharger with no variable nozzle.